Fragmentation of CO22+ in collisions with low-energy electrons

The fragmentation of the CO22+ dication following 200 eV electron impact double ionization was studied using a cold target recoil-ion momentum spectroscopy. Both two-body and three-body fragmentation channels were observed with an ion-ion coincidence technique. The slopes of the peaks in the coincidence spectra were extracted and compared with previous results and theoretical predictions. Overall, good agreement between theoretical and experimental results was achieved, while different behaviors were observed for the channel of fragmentation into C+ + O+ + O with previous high energy electron impact results. The momentum vectors of ionic fragments were measured, and thus the momentum vector of the neutral particle was deduced and kinetic energy release (KER) distributions for the different fragmentation channels were obtained. KER distribution behavior also shows a different signature from that induced by high energy electron impact. Furthermore, the three-body fragmentation mechanism, i.e., dissociation in one-or two-step processes, was distinguished from their distinct signatures on the Dalitz plots and the slopes of the islands from the covariance mapping spectrum. For example, the fragmentation channel C+ + O+ + O was found to be very similar to the 60 eV photon impact result [J. Laksman, E. P. Mansson, C. Grunewald, A. Sankari, M. Gisselbrecht, D. Ceolin, and S. L. Sorensen, J. Chem. Phys. 136, 104303 (2012)], which shows a predominant sequential dissociation process.